Referring to FIG. 1, identifying the various hosts and resources 13, 15 and 17-19, connected and available to a network 18 is a vital part of proper network management. Typically one host on the network is assigned the task of network manager ("NM") 10, running appropriate software, while the remaining hosts and resources are identified as agents. The manager 10 will periodically request information from the agents using one of a variety of protocols, e.g. Simple Network Manager Protocol ("SNMP") at the application layer, or Packet Internet Groper ("PING") at the IP layer, and expect a response from each agent using the same protocol. This process is referred to as "polling."
Efficient polling is becoming increasingly important with new bandwidth-intensive applications such as conferencing and web-push applications. Proper monitoring of the network can help deploy such applications. The collected traffic pattern of the network can be used to set and administer policies on application use, to configure intranet switches and routers, and to detect errant behavior. The challenge in polling is to be able to poll with high throughput, yet avoid intruding on the performance of user applications in the network.
Presently, the de facto network management software is marketed by Hewlett Packard under the trade name OpenView ("OV") and described more fully in R. Sturm, "Q&A", OpenView Advisor, pp. 11-13, 1(2) (March 1995), hereby incorporated by reference as if fully set forth herein. In operation, OV can transmit a maximum of N outstanding polls, where N is typically 3. For example, NM 10 may send a first poll to node 17. NM 10 will then wait a time-out period T.sub.1, for a response. If no response is received, a second poll is sent to node 17 and NM 10 will wait a time-out period 2.times.T.sub.1, for a response. This is repeated two more times with corresponding time-out periods of 4.times.T.sub.1 and 8.times.T.sub.1, respectively. NM 10 resends the poll these four times with continuously increasing time-out periods in order to rule out that the lack of a response is due to network traffic. If after four attempts no response to the polls is received, NM 10 concludes that node 17 is unavailable to the network.
It has been reported that the foregoing method of polling network resources is inefficient and leads to network "freeze up" as for example when a succession of nodes are unresponsive. See, A. B. Bondi, "A Nonblocking Mechanism for Regulating the transmission of Network Management Polls" IM '97, pp. 565-80 (May 1997), hereby incorporated by reference as if fully set forth herein. One proposed solution to ameliorate the deficiencies of the OV method is described in Bondi, supra. As described more fully therein, a minimum time threshold .tau. is set under which no two polls can be transmitted, while the maximum number of polls parameter N of OV is eliminated. As a result, freeze up is avoided by removing the constraint of N and network traffic is managed with constraint .tau.. However, even this proposal suffers from its inability to provide feedback relating to network congestion. The ability of a poller to quickly adapt to congestion is becoming increasingly important. Newer applications require continual monitoring, for example, at a rate of 5% of network capacity. Such monitoring can cause a network that is already congested with user traffic to collapse.